Switching circuit for luminous display tubes

ABSTRACT

In a switching circuit connected between a letter selecting circuit and a luminescent letter display tube there is provided a transistor for each anode electrode of the display tube. The base electrode of the transistor is qrounded, the emitter electrode is suitably biased, the collector electrode is connected to the anode electrode and the control signal is applied to the emitter electrode.

United States Patent Tatsuta 51 Apr. 11, 1972 SWITCHING CIRCUIT FORLUMINOUS References Cited DISPLAY TUBES UNITED STATES PATENTS [721Invent Tam, 156,131) 3,307,171 2/1967 Claessen ..340/324 [73] Assignee:ISE Electronics Corporation, lse, Jap 3,423,601 1/1969 Goodale ..307/2533,319,088 5/1967 Payne ..307/239 [221 Filed: 26, 1970 3,395,268 7/1968Barton ..340/324 [21] Appl' Nu: 67001 Primary Examiner-John W. CaldwellAssistant Examiner-Marshall M. Curtis Attorney-Chittick, Pfund, Birch,Samuels & Gauthier [30] Foreign Application Priority Data Sept. 1, 1969Japan ..44/68940 [57] ABSTRACT In a switching circuit connected betweena letter selecting cir- [52] us. Cl. ..340/324 R, 315/209, 340/334 suitand lumin n le er i play u e here is provided a [51] Int. Cl. ..G09f9/00 transistor f r h an ctrode of the display tube. The [58] F d Of Sar h --340/324 R, 334, 336; 315/845, ase electrode of the transistor isqrounded, the emitter elec- 315/846, 209; 307/239, 253 trode is suitablybiased, the collector electrode is connected to the anode electrode andthe control signal is applied to the emitter electrode. 1

2 Claims, 1 Drawing Figure PATENTEDAPR 11 I972 3,656 142 INVENTOR.

yosmo TATSUTA SWITCHING CIRCUIT FOR LUMINOUS DISPLAY TUBES BACKGROUND OFTHE INVENTION This invention relates to a switching circuit wherein atransistor is utilized to control a load by the switching action of thetransistor.

To display letters by controlling the combination of a plurality ofluminous electrodes of a fluorescent letter display tube it is necessaryto select suitable luminous electrodes corresponding to a letter to bedisplayed.

Although many types of selecting circuits for this purpose have beenproposed, usually a diode matrix circuit has been used.

To statically drive a fluorescent letter display tube (for brevity,hereinafter merely termed as display tube), it is usual to use a ratedanode voltage ranging form to volts so that it is easy to use aselecting circuit of the monolithic structure. However, in order todynamically drive the display tube it is necessary to set the anodevoltage to about 50 volts so that it is impossible to use a monolithicintegrated circuit.

To obviate this difficulty it has been proposed to provide a transistorbetween each one of the luminous electrodes and a letter selectingcircuit. However, this arrangement requires some modification of theletter selecting circuit. To avoid such modification two transistorshave been connected in cascade. However, this complicates the circuitconstruction.

SUMMARY OF THE INVENTION It is an object of this invention to provide asimple and economic switching circuit for display tubes.

According to this invention there is provided a transistor between aconventional letter selecting circuit and each anode electrode of aluminous letter display tube. The base electrode of the transistor isgrounded, the collector electrode is connected to the anode electrodeand the emitter electrode is suitably biased. The control signal fromthe letter selecting circuit is applied to the emitter electrode.Depending upon a particular digit or letter to be displayed, the letterselecting circuit operates to select a suitable combination of anodeelectrodes to operate transistors connected to the selected anodeelectrodes.

BRIEF DESCRIPTION OF THE DRAWING In the accompanying drawing a singlefigure shows a connection diagram of the switching circuit constructedaccording to the teaching of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to theaccompanying drawing a letter display tube 26 comprises a plurality ofluminous anode electrodes a through h, a grid electrode 27 and afilament electrode 25 energized by a filament source 29. As is wellknown in the art suitable combinations of anode electrodes a through hare selected by a selecting circuit, not shown, to selectively displayany one of digits 0, l, 2 9, for example.

Anode electrodes are controlled by PNP transistors 33a through 33h.Different from the prior art connection, the base electrodes of thesetransistors are grounded, emitter electrodes are suitably biased throughresistors 32a through 32h,

collector electrodes are connected to loads, that is anode electrodes athrough h and input signals from the letter selecting circuit areapplied to input terminals 34a through 34h which are connected toemitter electrodes. Anode electrodes 0 through h and collectorelectrodes of the transistors are connected to a source of positivepotential 28 through resistors 33a through 33h, respectively.

The switching circuit operates as follows. Assuming now that anodeelectrode a is to be operated, then a positive signal is applied toinput terminal 34a from the letter selecting circuit not shown. Thissignal creates a voltage drop across resistor 32a to positively bias theemitter electrode of transistor 31a to turn ON the same. Then thepositive potential of the source 28 is applied to the anode electrode aof the display tube 26 through the ground, resistor 32a and theemitter-collector circuit of transistor 31a, thus causing anode a toluminescence. At this time since no signal is applied to terminal 34hanode electrode h does not luminesce.

Although a voltage drop is created across resistor 320, since thecurrent flowing through it is very small and since its resistance valueis low (less than 1 kilo-ohms), ohms), provision of this resistor doesnot affect the brightness of the light emanated. Resistors 32a through32h may be replaced by level shift diodes of suitable polarity. Sincethe voltage drop is the same for all luminous electrodes, by slightlyincreasing the voltage of source 28 it is possible to produce uniformbrightness of the rated value.

For the sake of simplicity, in the foregoing description although theoperation of the anode a alone has been described, it will be clear thata suitable combination of anode electrodes is to be selected by theletter selecting circuit to display a desired digit.

Thus, according to this invention it is necessary to use only one typeof the letter selecting circuit thus greatly simplifying the circuitconstruction and saving the cost of manufacturing so as to improvereliability. The output from a bipolar integrated circuit now widelyused in many systems, such as table electronic computers and the likeprovides a positive output. A combination according to the presentinvention of the novel switching circuit and a letter selecting circuitis especially suitable to display digits on the fluorescent letterdisplay tube according to the output from such bipolar integratedcircuit.

Although a particular embodiment has been shown and described, it willbe clear that many modifications may be made without departing from thescope of the invention as defined in the appended claim.

What is claimed is:

1. In a switching circuit connected between a letter selecting circuitand a plurality of anode circuits of a luminous letter display tube, theimprovement which comprises for each said anode circuit, a singletransistor, means to ground the base electrode of said transistor, meansto connect each collector electrode to a respective anode electrode ofsaid display tube, means to bias the emitter electrode and means toapply a control signal from said letter selecting circuit to saidemitter electrode.

2. The switching circuit according to claim 1 wherein said display tubecomprises a plurality of luminous anode electrodes, said letterselecting circuits operate to select a suitable combination of saidanode electrode to display a given letter, and one of said transistor isprovided for each anode electrode and is of the PNP type.

1. In a switching circuit connected between a letter selecting circuitand a plurality of anode circuits of a luminous letter display tube, theimprovement which comprises for each said anode circuit, a singletransistor, means to ground the base electrode of said transistor, meansto connect each collector electrode to a respective anode electrode ofsaid display tube, means to bias the emitter electrode and means toapply a control signal from said letter selecting circuit to saidemitter electrode.
 2. The switching circuit according to claim 1 whereinsaid display tube comprises a plurality of luminous anode electrodes,said letter selecting circuits operate to select a suitable combinationof said anode electrode to display a given letter, and one of saidtransistor is provided for each anode electrode and is of the PNP type.